1. Field of the Invention
This invention relates to an apparatus for determining the alignment accuracy of an ophthalmic instrument, and in particular to an apparatus capable of determining the accuracy of alignment between a pre-aligned eye to be examined and ophthalmic instrument and further effecting fine adjustment of the alignment.
2. Description of the Prior Art
When a light flux is to be projected onto an eye to be examined to thereby measure the refractive power or the like of the eye, unless alignment of the ophthalmic instrument and the eye to be examined is accurately effected, a measurement error may not only occur but it also may not be possible to obtain a photograph for use as a determination material when it is desired to effect determination of characteristics of the eye with a photograph or the like. Therefore, in an ophthalmic instrument, for example, a target mark for alignment is projected onto the eye to be examined, a corneal-reflection image (virtual image) formed by corneal reflection is caused to be imaged in a television camera while, at the same time, a target mark fixed to the ophthalmic instrument is caused to be imaged on the same picture plane, and the two images are made coincident with each other, thereby accomplishing alignment.
However, when the eye to be examined is continually moving, an error may sometimes occur to the measurement value due to displacement resulting from a time delay until the measurement is made even if alignment is effected.